Lubricating oil composition

ABSTRACT

Provided is a lubricating oil composition for use in turbomachinery, compressors, hydraulic equipments, or machine tools, which contains a mineral oil (A) and a synthetic oil (B) containing a polyalkylene glycol (B1) and a polyol ester (B2), in which the content of the mineral oil (A) is 5 to 95% by mass based on the total amount of the lubricating oil composition, and which is used in turbomachinery, compressors, hydraulic equipments, or machine tools. The lubricating oil composition is excellent in oxidation stability, has a strong effect of preventing sludge precipitation and has excellent water separability even in use for a long period of time in high-temperature environments.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition used inturbomachinery, compressors, hydraulic equipments, or machine tools, anda method of using the lubricating oil composition.

BACKGROUND ART

A lubricating oil composition for use in instruments including variousturbomachinery such as steam turbines and gas turbines, compressors suchas rotary gas compressors and reciprocating compressors, hydraulicequipments, and hydraulic units of machine tools is used whilecirculating in a high-temperature environment system for a long periodof time.

When the lubricating oil composition is used for a long time under hightemperature environments, it is susceptible to sludge precipitationaccording to oxidative deterioration. The precipitated sludge adheresto, for example, a bearing of a rotor to generate heat, therebyproviding a risk of bearing damage, or may clog a filter arranged in acirculation line, or may deposit on a control valve, thereby oftencausing control system operation failures, etc.

Therefore, improvement in the effect of preventing sludge precipitationis required for the lubricating oil composition which is used whilecirculating in a high-temperature environment system for a long periodof time.

For example, PTL 1 discloses a lubricating oil composition for aircompressors, the composition including a synthetic base oil which is amixed oil of a polyglycol-based synthetic oil and an ester-basedsynthetic oil, and one or more amine-based antioxidants selected from aspecific compound group such as asymmetric diphenylamine-basedcompounds.

According to PTL 1, the lubricating oil composition for air compressorsshows a result of preventing sludge precipitation while appropriatelypreventing oxidation.

CITATION LIST Patent Literature

PTL 1: WO2013/146805

SUMMARY OF INVENTION Technical Problem

However, a lubricating oil composition used in instruments such asturbines which may be contaminated with water or steam is emulsified bycontamination with water or steam, which is a factor causing troubles ininstruments.

For this reason, the lubricating oil composition used in suchinstruments is required to be hardly emulsified and to be easilyseparated from water even when emulsified, that is, to be excellent inwater separability.

In PTL 1, studies have not been conducted on water separability of thelubricating oil composition.

An object of the present invention is to provide a lubricating oilcomposition excellent in oxidation stability and having a strong effectof preventing sludge precipitation even when used for a long period oftime under high temperature environments, and having excellent waterseparability, wherein the lubricating oil composition is used inturbomachinery, compressors, hydraulic equipments, or machine tools.

Solution to Problem

The present inventors have found that a lubricating oil compositioncontaining a mixed base oil that contains a combination of apredetermined mineral oil and a synthetic oil containing a polyalkyleneglycol (hereinafter also referred to as “PAG”) and a polyol ester(hereinafter also referred to as “POE”) can solve the above-mentionedproblems and have completed the present invention.

That is, the present invention provides the following [1] and [2].

[1] A lubricating oil composition containing a mineral oil (A) and asynthetic oil (B) that contains a polyalkylene glycol (B1) and a polyolester (B2);

in which the content of the mineral oil (A) is from 5 to 95% by massbased on the total amount of the lubricating oil composition, and

which is used in turbomachinery, compressors, hydraulic equipments, ormachine tools.

[2] A method of using a lubricating oil composition, using thelubricating oil composition of the above [1] in turbomachinery,compressors, hydraulic equipments, or machine tools.

Advantageous Effects of Invention

The lubricating oil composition of the present invention is excellent inoxidation stability, has a strong effect of preventing sludgeprecipitation and has excellent water separability, even when used for along period of time under high temperature environments. Consequently,the lubricating oil composition is suitable for use in turbomachinery,compressors, hydraulic equipments, or machine tools.

DESCRIPTION OF EMBODIMENTS

In the following description, kinematic viscosity and viscosity indexmean values measured and calculated in accordance with JIS K2283:2000.

The content of a phosphorus atom or a metal atom means a value measuredin accordance with JPI-5S-38-92.

The content of a nitrogen atom means a value measured in accordance withJIS K2609.

[Lubricating Oil Composition]

The lubricating oil composition of the present invention is used inturbomachinery, compressors, hydraulic equipments, or machine tools, andcontains a mineral oil (A) and a synthetic oil (B) that contains apolyalkylene glycol (PAG) (B1) and a polyol ester (POE) (B2).

The lubricating oil composition of the present invention uses, as a baseoil, a mixed base oil containing a synthetic oil that contains PAG andPOE, along with a mineral oil (A), and therefore can be excellent inoxidation stability, can have a strong effect of preventing sludgeprecipitation and can have excellent water separability, even when usedfor a long period of time under high temperature environments.

Mineral oil is excellent in water separability but is poor in oxidationstability in high-temperature environments and readily formsdeterioration materials, and the deterioration materials precipitate assludge to cause system troubles.

PAG has a property that dissolves deterioration materials to form inhigh-temperature environments and therefore prevents precipitation ofthe deterioration materials as sludge, but has a problem in waterseparability. In addition, since the polarity thereof is too high, PAGis poor in compatibility with an apolar base oil such as mineral oil,and therefore in a mixed base oil of a mineral oil and PAG, the two oilscould hardly exhibit a property of compensating for their drawbacks.

On the other hand, POE is poorer than PAG in point of solubility ofdeterioration materials that form in high-temperature environments, buthas a property of being excellent in compatibility with other base oils,and is therefore well compatible with both PAG and mineral oil. However,POE is also problematic in point of water separability.

Consequently, in the present invention, three kinds of base oils,mineral oil, PAG and POE are combined to provide a lubricating oilcomposition capable of expressing both the characteristic of “mineraloil” excellent in water separability and the characteristic of “PAG”capable of dissolving deterioration materials to form inhigh-temperature environments, in a well-balanced manner.

In the case where a base oil containing PAG and POE but not containing amineral oil is used, it still has a problem in point of waterseparability, and when any other additive is added thereto, the waterseparability of the resultant base oil tends to further decrease.

On the other hand, in the case where a base oil containing a mineral oiland POE but not containing PAG is used, the base oil is poorer than PAGalone in point of the ability to dissolve deterioration materials toform in high-temperature environments.

Further, in the case where a base oil containing a mineral oil and PAGbut not containing POE is used, the compatibility between the mineraloil and PAG is poor, and therefore the characteristic that the mineraloil has and the characteristic that PAG has could be hardly expressed.

In other words, in the present invention, three kinds of base oils,mineral oil, PAG and POE are combined, and therefore, while takingadvantages of their own characteristics, it is possible to compensatefor the disadvantageous of the individual base oil components by theother constituent base oils.

As a result, the lubricating oil composition of the present invention isexcellent in oxidation stability, has a strong effect of preventingsludge precipitation and has excellent water separability, even in usefor a long period of time in high-temperature environments.

From the viewpoint of providing such a lubricating oil composition thatis excellent in oxidation stability and has a strong effect ofpreventing sludge precipitation even in use for a long period of time inhigh-temperature environments, a lubricating oil composition of oneembodiment of the present invention preferably further contains anantioxidant (C) containing an amine-based antioxidant (C1).

Also from the viewpoint of improving wear resistance, a lubricating oilcomposition of one embodiment of the present invention preferablyfurther contains one or more phosphorus compounds (D) selected from aneutral phosphate (D1), an acid phosphate (D2) and an acid phosphateamine salt (D3).

With that, a lubricating oil composition of one embodiment of thepresent invention may contain any other lubricating oil additives thanthe components (C) and (D) within a range not detracting from theadvantageous effects of the present invention.

In the lubricating oil composition of one embodiment of the presentinvention, the total content of the components (A) and (B) is, based onthe total amount (100% by mass) of the lubricating oil composition,generally 65% by mass or more, preferably 70% by mass or more, morepreferably 80% by mass or more, even more preferably 90% by mass ormore, further more preferably 95% by mass or more, and is generally 100%by mass or less, preferably 99.9% by mass or less.

In the lubricating oil composition of one embodiment of the presentinvention, the total content of the components (A), (B), (C) and (D) is,based on the total amount (100% by mass) of the lubricating oilcomposition, preferably 70 to 100% by mass, more preferably 80 to 100%by mass, even more preferably 90 to 100% by mass, further morepreferably 97 to 100% by mass.

The components contained in the lubricating oil composition of oneembodiment of the present invention are described below.

<Mineral Oil (A)>

Examples of the mineral oil (A) for use in the present invention includetopped crudes obtained through atmospheric distillation of crude oilssuch as paraffin-based crude oils, intermediate-based crude oils andnaphthene-based crude oils; distillates obtained throughreduced-pressure distillation of such topped crudes; mineral oilsobtained by purifying the distillates through one or more purificationtreatments of solvent deasphalting, solvent extraction, hydrocracking,solvent dewaxing, catalytic dewaxing, or hydrorefining; and mineral oilwaxes obtained by isomerizing a wax produced from a natural gas throughFischer-Tropsch synthesis (GTL wax (Gas To Liquids WAX)).

One alone or two or more kinds of these mineral oils may be used eithersingly or as combined.

The mineral oil (A) for use in one embodiment of the present inventionis preferably a mineral oil grouped in Group 2 or 3 in the base oilcategory of API (American Petroleum Institute).

The kinematic viscosity at 40° C. of the mineral oil (A) for use in oneembodiment of the present invention is preferably 8 to 350 mm²/s, morepreferably 10 to 150 mm²/s, even more preferably 12 to 100 mm²/s,further more preferably 15 to 68 mm²/s.

The viscosity index of the mineral oil (A) for use in one embodiment ofthe present invention is preferably 80 or more, more preferably 90 ormore, even more preferably 100 or more.

In the lubricating oil composition of the present invention, the contentof the component (A) is, based on the total amount (100% by mass) of thelubricating oil composition, 5 to 95% by mass, preferably 10 to 95% bymass, more preferably 20 to 93% by mass, even more preferably 40 to 92%by mass, further more preferably 60 to 90% by mass.

When the content of the component (A) is less than 5% by mass, thelubricating oil composition is poor in water separability and especiallywhen various additives are added thereto, reduction in waterseparability of the composition may be greater.

On the other hand, when the content of the component (A) is more than95% by mass, the content of the components (B1) and (B2) could not besecured sufficiently and, if so, sludge precipitation readily occurs inhigh-temperature environments and the lubricating oil composition ispoor in oxidation stability.

In the lubricating oil of one embodiment of the present invention, thecontent ratio of the component (A) to the total content of the component(B1) and the component (B2) [(A)/(B1)+(B2)] is, by mass, from theviewpoint of providing a lubricating oil composition excellent in waterseparability, preferably 0.05 or more, more preferably 0.10 or more,even more preferably 0.30 or more, further more preferably 0.70 or more,further more preferably 1.50 or more, especially more preferably 3.50 ormore, and is, from the viewpoint of providing a lubricating oilcomposition excellent in oxidation stability and having a strong effectof preventing sludge precipitation even in use for a long period of timein high-temperature environments, preferably 19.0 or less, morepreferably 15.0 or less, even more preferably 12.0 or less.

<Synthetic Oil (B)>

The synthetic oil (B) contained in the lubricating oil composition ofthe present invention contains a polyalkylene glycol (B1) and a polyolester (B2).

The synthetic oil (B) for use in one embodiment of the present inventionmay further contain any other synthetic oil than the components (B1) and(B2) within a range not detracting from the advantageous effects of thepresent invention.

However, in the lubricating oil composition of one embodiment of thepresent invention, the total content of the components (B1) and (B2) inthe synthetic oil (B) is, based on the total amount (100% by mass) ofthe synthetic oil (B) contained in the lubricating oil composition,preferably 70 to 100% by mass, more preferably 80 to 100% by mass, evenmore preferably 90 to 100% by mass, further more preferably 95 to 100%by mass.

In the lubricating oil composition of one embodiment of the presentinvention, the content ratio of the component (B1) to the component (B2)[(B1)/(B2)] is, by mass, from the viewpoint of providing a lubricatingoil composition excellent in oxidation stability and having a strongeffect of preventing sludge precipitation even in use for a long periodof time in high-temperature environments, preferably 10/90 to 80/20,more preferably 15/85 to 70/30, even more preferably 20/80 to 60/40,further more preferably 25/75 to 55/45.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (B) is, based on the totalamount (100% by mass) of the lubricating oil composition, from theviewpoint of providing a lubricating oil composition excellent inoxidation stability and having a strong effect of preventing sludgeprecipitation even in use for a long period of time in high-temperatureenvironments, preferably 5% by mass or more, more preferably 6% by massor more, even more preferably 7% by mass or more, further morepreferably 8% by mass or more, and is, from the viewpoint of providing alubricating oil composition excellent in water separability, preferably95% by mass or less, more preferably 90% by mass or less, even morepreferably 80% by mass or less, further more preferably 60% by mass orless, further more preferably 40% by mass or less, especially morepreferably 20% by mass or less.

[Polyalkylene Glycol (B1)]

Examples of the polyalkylene glycol (B1) include polymers obtained bypolymerization or copolymerization of alkylene oxide.

Further, the polyalkylene glycol (B1) may be used alone or incombination of two or more kinds thereof.

A number average molecular weight (Mn) of the polyalkylene glycol (B1)used in one embodiment of the present invention is preferably 200 to10,000, more preferably 240 to 5,000, still more preferably 280 to3,000, and even still more preferably 320 to 1,500 from the viewpoint ofimproving the viscosity index of the lubricating oil composition.

In this description, the number average molecular weight (Mn) is a valueas expressed in terms of standard polystyrene, measured by gelpermeation chromatography (GPC), and measurement conditions includeconditions described in Examples.

Further, the polyalkylene glycol (B1) used in one embodiment of thepresent invention is preferably a polyalkylene glycol in which at leastone end is sealed with a substituent, from the viewpoint of providing alubricating oil composition which is further improved in the effect ofpreventing sludge precipitation.

Examples of the substituent capable of sealing the end of thepolyalkylene glycol include a monovalent hydrocarbon group having 1 to10 carbon atoms, an acyl group having 2 to 10 carbon atoms, or aheterocyclic group having 3 to 10 ring atoms, and preferably, amonovalent hydrocarbon group having 1 to 10 carbon atoms.

Further, examples of specific groups regarding the monovalenthydrocarbon group, acyl group, and heterocyclic group that can beselected as the substituent, and the range of the preferable number ofthe carbon atoms or ring atoms is the same as defined in R^(B1) andR^(B3) in the following formula (b-1).

In one embodiment of the present invention, the polyalkylene glycol (B1)is preferably a compound represented by the following general formula(b-1), from the viewpoint of providing a lubricating oil compositionwhich is further improved in the effect of preventing sludgeprecipitation.

R^(B1)—[(OR^(B2))_(n)—OR^(B3)]_(b)  (b-1)

In the general formula (b-1), R^(B1) is a hydrogen atom, a monovalenthydrocarbon group having 1 to 10 carbon atoms, an acyl group having 2 to10 carbon atoms, a divalent to hexavalent hydrocarbon group having 1 to10 carbon atoms, or a heterocyclic group having 3 to 10 ring atoms.

R^(B2) is an alkylene group having 2 to 4 carbon atoms.

R^(B3) is a hydrogen atom, a monovalent hydrocarbon group having 1 to 10carbon atoms, an acyl group having 2 to 10 carbon atoms, or aheterocyclic group having 3 to 10 ring atoms.

b is an integer of 1 to 6, preferably an integer of 1 to 4, morepreferably 1 to 3, and still more preferably 1.

Further, b is determined according to the number of the binding sitewith R^(B1) in the general formula (b-1).

For example, when R^(B1) is a monovalent hydrocarbon group such as analkyl group or a cycloalkyl group, or an acyl group, b is 1. In otherwords, when R^(B1) is a hydrocarbon group or a heterocyclic group, andthe valence of the group is 1, 2, 3, 4, 5, and 6, b is 1, 2, 3, 4, 5 and6, respectively.

a is a number of 1 or more, and is a value appropriately determinedaccording to the value of the number average molecular weight of thecompound represented by the general formula (b-1).

Further, when two or more different kinds of the compound represented bygeneral formula (b-1) are used, a is an average value (a weightedaverage value), and the average value may be 1 or more.

Further, when there are a plurality of R^(B2) and R^(B3), R^(B2) andR^(B3) may be the same as or different from each other.

In one embodiment of the present invention, at least one of R^(B1) andR^(B3) in the general formula (b-1) is preferably a monovalenthydrocarbon group having 1 to 10 carbon atoms, an acyl group having 2 to10 carbon atoms, a divalent to hexavalent hydrocarbon group having 1 to10 carbon atoms, or a heterocyclic group having 3 to 10 ring atoms, andmore preferably a monovalent hydrocarbon group having 1 to 10 carbonatoms.

Examples of the monovalent hydrocarbon group having 1 to 10 carbon atomswhich can be selected as R^(B1) and R^(B3) include alkyl groups such asa methyl group, an ethyl group, a propyl group (a n-propyl group, anisopropyl group), a butyl group (a n-butyl group, an isobutyl group, ans-butyl group, a t-butyl group), a pentyl group, a hexyl group, a heptylgroup, an octyl group, a nonyl group, and a decyl group; cycloalkylgroups such as a cyclopentyl group, a cyclohexyl group, amethylcyclohexyl group, an ethylcyclohexyl group, a propylcyclohexylgroup, and a dimethyl cyclohexyl group; aryl groups such as a phenylgroup, a methylphenyl group, an ethylphenyl group, a dimethyl phenylgroup, a propyl phenyl group, a trimethylphenyl group, a butylphenylgroup, and a naphthyl group; arylalkyl groups such as a benzyl group, aphenylethyl, a methylbenzyl group, a phenylpropyl group, and aphenylbutyl group.

Further, the alkyl group may be either linear or branched.

The number of carbon atoms of the monovalent hydrocarbon group ispreferably 1 to 10, more preferably 1 to 6, and still more preferably 1to 4.

The hydrocarbon group moiety in the acyl group having 2 to 10 carbonatoms which can be selected as R^(B1) and R^(B3) may be linear,branched, or cyclic. The hydrocarbon group moiety includes those having1 to 9 carbon atoms among the monovalent hydrocarbon groups which can beselected as R^(B1) and R^(B3).

Further, the number of carbon atoms of the acyl group is preferably 2 to10, and more preferably 2 to 6.

The divalent to hexavalent hydrocarbon group which can be selected asR^(B1) includes residues obtained by removing 1 to 5 hydrogen atoms fromthe monovalent hydrocarbon group which can be selected as R^(B1) andresidues obtained by removing a hydroxy group from polyhydric alcohols,such as trimethylolpropane, glycerin, pentaerythritol, sorbitol,1,2,3-trihydroxycyclohexane, and 1,3,5-trihydroxycyclohexane.

Further, the number of carbon atoms of the divalent to hexavalenthydrocarbon group is preferably 1 to 10, more preferably 1 to 6, andstill more preferably 1 to 4.

The heterocyclic group having 3 to 10 ring atoms which can be selectedas R^(B1) and R^(B3) is preferably an oxygen atom-containingheterocyclic group or a sulfur atom-containing heterocyclic group.Further, the heterocyclic group may be a saturated ring or anunsaturated ring.

Examples of the oxygen atom-containing heterocyclic group includeresidues obtained by removing 1 to 6 hydrogen atoms from an oxygenatom-containing saturated heterocyclic ring, such as 1,3-propyleneoxide, tetrahydrofuran, tetrahydropyran, and hexamethylene oxide, and anoxygen atom-containing unsaturated heterocyclic ring, such as acetyleneoxide, furan, pyran, oxycycloheptatriene, isobenzofuran, andisochromene.

Examples of the sulfur atom-containing heterocyclic group includeresidues obtained by removing 1 to 6 hydrogen atoms from a sulfuratom-containing saturated heterocyclic ring, such as ethylene sulfide,trimethylene sulfide, tetrahydrothiophene, tetrahydrothiopyran, andhexamethylene sulfide, and a sulfur atom-containing unsaturatedheterocyclic ring, such as acetylene sulfide, thiophene, thiapyran, andthiotripyridene.

The number of ring atoms of the heterocyclic group is preferably 3 to10, more preferably 3 to 6, and still more preferably 5 or 6.

Examples of the alkylene group having 2 to 4 carbon atoms that can beselected as R^(B2) include an alkylene group having 2 carbon atoms, suchas an ethylene group (—CH₂CH₂—); an alkylene group having 3 carbonatoms, such as a trimethylene group (—CH₂CH₂CH₂—), a 1-methylethylenegroup (a propylene group) (—CH(CH₃)CH₂—); and an alkylene group having 4carbon atoms, such as a tetramethylene group (—CH₂CH₂CH₂CH₂—), a1-methyltrimethylene group (—CH(CH₃)CH₂CH₂—), a 2-methyltrimethylenegroup (—CH₂CH(CH₃)CH₂—), a butylene group (—C(CH₃)₂CH₂—), a1-ethylethylene group (—CH(CH₂CH₃)CH₂—, and a 1,2-dimethylethylene group(—CH(CH₃)—CH(CH₃)—).

Further, when there are a plurality of R^(B2)'s, R^(B2)'s may be thesame as each other or may be a combination of two or more kinds ofalkylene groups.

Among them, R^(B2) is preferably an ethylene group (—CH₂CH₂—) or a1-methylethylene group (propylene group) (—CH(CH₃)CH₂—).

In the compound represented by the general formula (b-1), the content ofthe oxypropylene unit (—OCH(CH₃)CH₂—) is preferably 50% by mol to 100%by mol, more preferably 65% by mol to 100% by mol, and still morepreferably 80% by mol to 100% by mol, based on the total amount (100% bymol) of the oxyalkylene unit (OR^(B2)) in the structure of the compound.

The kinematic viscosity at 40° C. of the component (B1) used in oneembodiment of the present invention is preferably 8 mm²/s to 350 mm²/s,more preferably 10 mm²/s to 150 mm²/s, still more preferably 12 mm²/s to100 mm²/s, and even still more preferably 15 mm²/s to 68 mm²/s.

Further, the viscosity index of the component (B1) used in oneembodiment of the present invention is preferably 90 or more, morepreferably 100 or more, still more preferably 120 or more, and evenstill more preferably 140 or more.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (B1) is, based on the totalamount (100% by mass) of the lubricating oil composition, preferably 1.0to 70% by mass, more preferably 1.2 to 50% by mass, even more preferably1.4 to 30% by mass, further more preferably 1.5 to 20% by mass, furthermore preferably 1.7 to 12% by mass, and especially more preferably 1.9to 6% by mass.

[Polyol Ester (B2)]

Examples of the polyol ester (B2) include a hindered ester of a hinderedpolyol, which has one or more quaternary carbon atoms in the moleculewherein at least one of the quaternary carbon atoms has 1 to 4 methylolgroups bonded thereto, with an aliphatic monocarboxylic acid.

The polyol ester (B2) may be used alone or in combination of two or morekinds thereof.

Further, the polyol ester (B2) is generally a complete ester in whichall the hydroxy groups of the polyol are esterified, but may include apartial ester in which some of the hydroxy groups remain unesterified,as long as the effects of the present invention are not impaired.

The hindered polyol is preferably a compound represented by thefollowing general formula (b-2).

In the general formula (b-2), R^(B11) and R^(B12) are each independentlya monovalent hydrocarbon group having 1 to 6 carbon atoms or a methylolgroup (—CH₂OH).

n represents an integer of 0 to 4, preferably 0 to 2, more preferably 0or 1, and still more preferably 0. When n=0, it is a single bond andprovides a compound represented by the following general formula (b-2′).

In the general formula (b-2′), R^(B11) and R^(B12) each independentlyrepresent a monovalent hydrocarbon group having 1 to 6 carbon atoms or amethylol group (—CH₂OH).

Examples of the monovalent hydrocarbon group having 1 to 6 carbon atomswhich can be selected as R^(B11) and R^(B12) include alkyl groups having1 to 6 carbon atoms (a methyl group, an ethyl group, a propyl group, abutyl group, a pentyl group, a hexyl group), a cyclopentyl group, acyclohexyl group, and a phenyl group.

Further, the alkyl group may be either linear or branched.

Among them, the monovalent hydrocarbon group having 1 to 6 carbon atomswhich can be selected as R^(B11) and R^(B12) is preferably an alkylgroup having 1 to 6 carbon atoms, and more preferably an alkyl grouphaving 1 to 3 carbon atoms.

Examples of the compound represented by the following general formula(b-2) include a hindered polyol such as a dialkylpropanediol (whereinthe alkyl group has 1 to 6 carbon atoms), a trimethylolalkane (whereinthe alkane has 2 to 7 carbon atoms), and a pentaerythritol, and adehydrated condensate thereof, and more specifically, neopentyl glycol,2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl 1,3-propanediol,trimethylolethane, trimethylolpropane, trimethylolbutane,trimethylolpentane, trimethylolhexane, trimethylolheptane,pentaerythritol, 2,2,6,6-tetramethyl-4-oxa-1,7-heptanediol,2,2,6,6,10,10-hexamethyl-4,8-dioxa-1,11-undecadiol,2,2,6,6,10,10,14,14-octamethyl-4,8,12-trioxa-1,15-pentadecadiol,2,6-di(hydroxymethyl)-2,6-dimethyl-4-oxa-1,7-heptanediol,2,6,10-tri(hydroxymethyl)-2,6,10-trimethyl-4,8-dioxa-1,11-undecadiol,2,6,10,14-tetra(hydroxymethyl)-2,6,10,14-tetramethyl-4,8,12-trioxa-1,15-pentadecadiol,di(pentaerythritol), tri(pentaerythritol), tetra(pentaerythritol), andpenta(pentaerythritol).

Among them, trimethylolpropane, neopentyl glycol, pentaerythritol, andbimolecular or trimolecular dehydrated condensates thereof arepreferred, and trimethylolpropane, neopentyl glycol, and pentaerythritolare more preferred, and trimethylolpropane is still more preferred.

The aliphatic monocarboxylic acid includes a saturated aliphaticmonocarboxylic acid having 5 to 22 carbon atoms.

The acyl group of the saturated aliphatic monocarboxylic acid may beeither linear or branched.

Examples of the saturated aliphatic monocarboxylic acid include a linearsaturated monocarboxylic acid such as valeric acid, caproic acid,enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoicacid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid,palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid,arachic acid, and behenic acid; and a branched saturated monocarboxylicacid such as isomyristic acid, isopalmitic acid, isostearic acid,2,2-dimethylpropanoic acid, 2,2-dimethylbutanoic acid,2,2-dimethylpentanoic acid, 2,2-dimethyloctanoic acid,2-ethyl-2,3,3-trimethylbutanoic acid, 2,2,3,4-tetramethylpentanoic acid,2,5,5-trimethyl-2-t-butylhexanoic acid, 2,3,3-trimethyl-2-ethylbutanoicacid, 2,3-dimethyl-2-isopropylbutanoic acid, 2-ethylhexanoic acid, and3,5,5-trimethylhexanoic acid.

In esterification, these aliphatic monocarboxylic acids may be usedalone or in combination of two or more kinds thereof.

The number of carbon atoms of the saturated aliphatic monocarboxylicacid is preferably 5 to 18, more preferably 6 to 14, and still morepreferably 8 to 10.

The kinematic viscosity at 40° C. of the polyol ester (B2) used in oneembodiment of the present invention is preferably 8 mm²/s to 350 mm²/s,more preferably 10 mm²/s to 150 mm²/s, still more preferably 11 mm²/s to100 mm²/s, and even still more preferably 12 mm²/s to 68 mm²/s.

Further, the viscosity index of the polyol ester (B2) used in oneembodiment of the present invention is preferably 90 or more, morepreferably 100 or more, still more preferably 110 or more, and evenstill more preferably 120 or more.

The number average molecular weight (Mn) of the polyol ester (B2) usedin one embodiment of the present invention is preferably 100 to 8,000,more preferably 200 to 4,000, still more preferably 300 to 2,000, andeven still more preferably 400 to 1,000.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (B2) is, based on the totalamount (100% by mass) of the lubricating oil composition, preferably 2.0to 90% by mass, more preferably 2.5 to 70% by mass, even more preferably3.0 to 55% by mass, further more preferably 3.5 to 40% by mass, furthermore preferably 4.0 to 30% by mass, and especially more preferably 4.5to 15% by mass.

[Synthetic Oil other than Components (B1) and (B2)]

The synthetic oil (B) for use in one embodiment of the present inventionmay further contain any other synthetic oil than the components (B1) and(B2) within a range not detracting from the advantageous effects of thepresent invention.

Examples of the other synthetic oil include poly-α-olefins such asα-olefin homopolymers or α-olefin copolymers (for example, α-olefincopolymers having 8 to 14 carbon atoms such as ethylene-α-olefincopolymers); isoparaffin; various esters other than the component (B2),such as dibasic acid esters (for example, ditridecyl glutarate),aromatic acid esters (for example, 2-ethylhexyl trimellitate,2-ethylhexyl pyromellitate), and phosphate esters; various ethers otherthan the component (B1), such as polyphenyl ethers; alkylbenzenes; andalkylnaphthalenes.

One alone or two or more kinds of these synthetic oils may be usedeither singly or as combined.

<Antioxidant (C)>

The lubricating oil composition of one embodiment of the presentinvention preferably contains an antioxidant (C) containing anamine-based antioxidant (C1), from the viewpoint of providing alubricating oil composition which is excellent in oxidation stability,suppresses generation of deterioration products, and is further improvedin the effect of preventing sludge precipitation.

The antioxidant (C) used in one embodiment of the present invention mayfurther contain any other antioxidant than the amine-based antioxidant(C1) together with the amine-based antioxidant (C1).

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (C1) in the component (C) is,based on the total amount (100% by mass) of the component (C),preferably 30 to 100% by mass, more preferably 50 to 100% by mass, evenmore preferably 60 to 100% by mass, and further more preferably 70 to100% by mass, from the viewpoint of providing a lubricating oilcomposition which suppresses generation of deterioration products, isfurther improved in the effect of preventing sludge precipitation, andhas excellent oxidation stability.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (C) is preferably 0.01 to 10% bymass, more preferably 0.05 to 7% by mass, and still more preferably 0.1to 5% by mass, based on the total amount (100% by mass) of thelubricating oil composition, from the viewpoint of providing alubricating oil composition which suppresses generation of deteriorationproducts, is further improved in the effect of preventing sludgeprecipitation, and has excellent oxidation stability.

[Amine-based Antioxidant (C1)]

The amine-based antioxidant (C1) may be an amine-based compound havingantioxidant performance, and includes naphthylamine (C11) anddiphenylamine (C12).

The amine-based antioxidant (C1) may be used alone or in combination oftwo or more kinds thereof.

Further, in one embodiment of the present invention, both naphthylamine(C11) and diphenylamine (C12) are preferably included.

In the lubricating oil composition of one embodiment of the presentinvention, the content ratio [(C11)/(C12)] of the naphthylamine (C11)and the diphenylamine (C12) is preferably 10/90 to 90/10, morepreferably 15/85 to 85/15, still more preferably 20/80 to 80/20, andeven still more preferably 25/75 to 75/25 by a mass ratio.

Examples of the naphthylamine (C11) include phenyl-α-naphthylamine,phenyl-β-naphthylamine, alkylphenyl-α-naphthylamine, andalkylphenyl-β-naphthylamine, and preferably, alkylphenyl-α-naphthylamineand alkylphenyl-β-naphthylamine.

The number of carbon atoms of the alkyl group in thealkylphenyl-α-naphthylamine and the alkylphenyl-β-naphthylamine ispreferably 1 to 30, but is, from the viewpoint of improving solubilitywith the mineral oil (A) and the synthetic oil (B), and more improvingthe effect of preventing sludge precipitation, more preferably 1 to 20,even more preferably 4 to 16, and still more preferably 6 to 14.

The diphenylamine (C12) is preferably a compound represented by thefollowing general formula (c-1) and more preferably a compoundrepresented by the following general formula (c-2).

In the general formulae (c-1) and (c-2), R^(x) and R^(y) are eachindependently an alkyl group having 1 to 30 carbon atoms, or an alkylgroup having 1 to 30 carbon atoms substituted with an aryl group having6 to 18 ring atoms.

The alkyl group may be either a linear alkyl group or a branched alkylgroup.

In general formula (c-1), z1 and z2 are each independently an integer of0 to 5, preferably 0 or 1, and more preferably 1. Further, when thereare a plurality of R^(x) and R^(y), R^(x) and R^(y) may be the same asor different from each other.

Further, the number of carbon atoms of the alkyl group which can beselected as R^(x) and R^(y) is 1 to 30, preferably 1 to 20, and morepreferably 1 to 10.

Examples of the aryl group that can be substituted for the alkyl groupinclude a phenyl group, a naphthyl group, and a biphenyl group, andpreferably, a phenyl group.

Examples of the alkyl group in the alkylphenyl-naphthylamine and thealkyl group in the diphenylamine include a methyl group, an ethyl group,a propyl group, a butyl group, a pentyl group, a hexyl group, a heptylgroup, an octyl group, a nonyl group, a decyl group, an undecyl group, adodecyl group, a hexadecyl group, an octadecyl group, a nonadecyl group,an eicosyl group, and a tetracosyl group.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the amine-based antioxidant (C1) in terms ofnitrogen atom is preferably 50 to 3000 ppm by mass, more preferably 100to 2000 ppm by mass, still more preferably 120 to 1500 ppm by mass, evenstill more preferably 150 to 1000 ppm by mass, based on the total amount(100% by mass) of the lubricating oil composition, from the viewpoint ofproviding a lubricating oil composition which suppresses generation ofdeterioration products, is further improved in the effect of preventingsludge precipitation, and has excellent oxidation stability.

[Antioxidant other than amine-based antioxidant (C1)]

The antioxidant (C) may also contain an antioxidant other than the aboveamine-based antioxidant (C1). As such an antioxidant, a phenol-basedantioxidant is preferred.

Examples of the phenol-based antioxidant include monocyclic phenolcompounds such as 2,6-di-t-butyl-4-methylphenol,2,6-di-t-butyl-4-ethylphenol, 2,4,6-tri-t-butylphenol,2,6-di-t-butyl-4-hydroxymethylphenol, 2,6-di-t-butylphenol,2,4-dimethyl-6-t-butylphenol,2,6-di-t-butyl-4-(N,N-dimethylaminomethyl)phenol,2,6-di-t-amyl-4-methylphenol, andn-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate; and polycyclicphenol compounds such as 4,4′-methylenebis(2,6-di-t-butylphenol),4,4′-isopropylidenebis(2,6-cli-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylphenol),4,4′-bis(2,6-di-t-butylphenol), 4,4′-bis(2-methyl-6-t-butylphenol),2,2′-methylenebis(4-ethyl-6-t-butylphenol), and4,4′-butylidenebis(3-methyl-6-t-butylphenol).

In the lubricating oil composition of one embodiment of the presentinvention, the content of the phenol-based antioxidant relative to 100parts by mass of the amine-based antioxidant (C1) is preferably 0 partby mass to 100 parts by mass, more preferably 0 part by mass to 60 partsby mass, and still more preferably 0 part by mass to 40 parts by mass.

<Phosphorus Compound (D)>

The lubricating oil composition of one embodiment of the presentinvention preferably further contains one or more phosphorus compounds(D) selected from a neutral phosphate (D1), an acid phosphate (D2), anacid phosphate amine salt (D3) and a sulfur-phosphorus compound (D4),from the viewpoint of improving wear resistance.

From the viewpoint of further improving rust-preventing performance, thecomponent (D) preferably contains one or more selected from thecomponent (D1) and the component (D3). Also from the viewpoint ofsatisfying both oxidation stability and wear resistance even in arelatively small amount, the component (D) preferably contains one ormore selected from the component (D3) and the component (D4).

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (D) in terms of phosphorus atomis, based on the total amount (100% by mass) of the lubricating oilcomposition, preferably 10 to 1600 ppm by mass, more preferably 20 to1200 ppm by mass, even more preferably 50 to 1000 ppm by mass, furthermore preferably 100 to 800 ppm by mass, especially more preferably 150to 600 ppm by mass. In the case where one or more selected from thecomponent (D3) and the component (D4) are used, the content thereof interms of phosphorus atom may be, based on the total amount (100% bymass) of the lubricating oil composition, preferably 10 to 50 ppm bymass, more preferably 10 to 30 ppm by mass.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the component (D) is, based on the totalamount (100% by mass) of the lubricating oil composition, preferably0.01 to 2.0% by mass, more preferably 0.02 to 1.5% by mass, even morepreferably 0.05 to 1.0% by mass, further more preferably 0.10 to 0.70%by mass. When one or more selected from the component (D3) and thecomponent (D4) are used, the content of the component (D) may be, basedon the total amount (100% by mass) of the lubricating oil composition,preferably 0.01 to 1.0 ppm by mass, more preferably 0.01 to 0.2 ppm bymass, even more preferably 0.01 to 0.05 ppm by mass.

[Neutral Phosphate (D1)]

The neutral phosphate (D1) is preferably a compound (D11) represented bythe following general formula (d1-1).

In the general formula (d1-1), R^(D1) to R^(D3) are each independentlyan alkyl group having 1 to 18 (preferably 3 to 18) carbon atoms, or anaryl group having 6 to 18 ring carbon atoms and substituted with analkyl group having 1 to 18 (preferably 3 to 12) carbon atoms.

Examples of the alkyl group having 1 to 18 carbon atoms which can beselected as R^(D1) to R^(D3) include a methyl group, an ethyl group, apropyl group (a n-propyl group, an isopropyl group), a butyl group (an-butyl group, an s-butyl, a t-butyl group, an isobutyl group), a pentylgroup, a hexyl group, a 2-ethyl hexyl group, a heptyl group, an octylgroup, a nonyl group, a decyl group, an undecyl group, a dodecyl group,a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecylgroup, a heptadecyl group, and an octadecyl group.

These alkyl group may be either a linear alkyl group or a branched alkylgroup.

Examples of the aryl group having 6 to 18 ring carbon atoms include aphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, abiphenyl group, a terphenyl group, and a phenylnaphthyl group, andpreferably, a phenyl group.

The “aryl group substituted with an alkyl group having 1 to 18 carbonatoms” which can be selected as R^(D1) to R^(D3) includes a group inwhich at least one of hydrogen atoms bonded to the ring carbon atoms ofthe aryl group is substituted with the alkyl group having 1 to 18 carbonatoms.

The compound (D11) is more preferably a compound (D12) represented bythe following general formula (d1-2).

In the general formula (d1-2), R^(D11) to R^(D13) are each independentlyan alkyl group having 1 to 18 carbon atoms. The alkyl group may be thesame as the alkyl group which can be selected as R^(D11) to R^(D13).

The number of carbon atoms of the alkyl group which can be selected asR¹¹ to R¹³ is 1 to 18 but is, from the viewpoint of providing alubricating oil composition having improved rust-preventing performance,preferably 3 to 12, more preferably 3 to 8, even more preferably 3 to 6,further more preferably 3.

p1 to p3 are each independently an integer of 1 to 5, preferably aninteger of 1 to 2, and more preferably 1.

[Acid Phosphate (D2)]

The acid phosphate (D2) is preferably one or more selected from acompound represented by the following general formula (d2-1) and acompound represented by the following general formula (d2-2).

In the general formulae (d2-1) and (d2-2), R^(a) and R^(b) are eachindependently an alkyl group having 1 to 12 carbon atoms. The alkylgroup may be the same as the alkyl group having 1 to 12 carbon atomsamong the alkyl group which can be selected as R^(D1) to R^(D3) asmentioned above.

The number of carbon atoms of the alkyl group which can be selected asR^(a) and R^(b) is preferably 3 to 10, more preferably 6 to 10, andstill more preferably 8 to 10.

R^(a) and R^(b) in the general formula (d2-1) may be the same as ordifferent from each other.

[Acid Phosphate Amine Salt (D3)]

The acid phosphate amine salt (D3) is preferably one or more selectedfrom an amine salt of a compound represented by the above-mentionedgeneral formula (d2-1) and an amine salt of a compound represented bythe above-mentioned general formula (d2-2).

The amine to form the amine salt is preferably a compound represented bythe following general formula (d3). One alone or two or more kinds ofthe amines may be used either singly or as combined.

(R^(c))_(q)—N—(H)_(3−q)  (d3)

In the general formula (d3), q represents an integer of 1 to 3.

R^(C) is each independently an alkyl group having 6 to 18 carbon atoms,an alkenyl group having 6 to 18 carbon atoms, an aryl group having 6 to18 ring carbon atoms, an arylalkyl group having 7 to 18 carbon atoms, ora hydroxyalkyl group having 6 to 18 carbon atoms, and preferably, analkyl group having 6 to 18 carbon atoms.

When there are a plurality of R^(C)s, R^(C)s may be the same as ordifferent from each other.

Examples of the alkyl group which can be selected as R^(C) include ahexyl group, a heptyl group, an octyl group, a 2-ethylhexyl group, anonyl group, a decyl group, an undecyl group, a dodecyl group, atridecyl group, a tetradecyl group, a hexadecyl group, and an octadecylgroup.

The alkyl group may be either a linear alkyl group or a branched alkylgroup.

The number of carbon atoms of the alkyl group which can be selected asR^(C) is 6 to 18, preferably 7 to 16, more preferably 8 to 15, and stillmore preferably 10 to 13.

Examples of the alkenyl group which can be selected as R^(C) include ahexenyl group, a heptenyl group, an octenyl group, a nonenyl group, adecenyl group, an undecenyl group, a dodecenyl group, a tridecenylgroup, a tetradecenyl group, a hexadecenyl group, and an octadecenylgroup.

The alkenyl group may be either a linear alkenyl group or a branchedalkenyl group.

The number of carbon atoms of the alkenyl group which can be selected asR^(C) is 6 to 18, preferably 7 to 16, more preferably 8 to 15, and stillmore preferably 10 to 13.

Examples of the aryl group which can be selected as R^(C) include aphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, abiphenyl group, a terphenyl group, and a phenylnaphthyl group.

The number of carbon atoms of the aryl group which can be selected asR^(C) is 6 to 18, preferably 6 to 16, and more preferably 6 to 14.

The arylalkyl group which can be selected as R^(C) includes a group inwhich a hydrogen atom of the alkyl group is substituted with the arylgroup, and specifically, a phenylmethyl group, and a phenylethyl group.

The number of carbon atoms of the arylalkyl group which can be selectedas R^(C) is 7 to 18, preferably 7 to 16, and more preferably 8 to 14.

The hydroxyalkyl group which can be selected as R^(C) includes a groupin which a hydrogen atom of the alkyl group is substituted with ahydroxy group, and specifically, a hydroxyhexyl group, a hydroxyoctylgroup, a hydroxydodecyl group, and a hydroxytridecyl group.

The number of carbon atoms of the hydroxyalkyl group which can beselected as R^(C) is 6 to 18, preferably 7 to 16, more preferably 8 to15, and still more preferably 10 to 13.

[Sulfur-Phosphorus Compound (D4)]

The sulfur-phosphorus compound (D4) includes monothiophosphates,dithiophosphates, trithiophosphates, monothiophosphate amine salts,dithiophosphate amine salts, monothiophosphites, dithiophosphites, andtrithiophosphites, and among these, dithiophosphates are preferred.

From the viewpoint of bettering wear resistance, dithiophosphates havinga carboxy group or an ester residue at the terminal are preferred amongdithiophosphates. Having a carboxy group or an ester group at theterminal, the sulfur-phosphorus compound (D4) can have high polarity,and therefore also in this embodiment using the above-mentioned specificester-based synthetic base oil (A) as a base oil, the sulfur-phosphoruscompound of the type can readily exhibit a function as an extremepressure agent.

Specific examples of the dithiophosphate having a carboxy group or anester residue at the terminal include compounds represented by thefollowing general formula (d4).

In the formula (d4), R^(d) represents a linear or branched alkylenegroup having 1 to 8 carbon atoms, R^(e) and R^(f) each independentlyrepresent a hydrocarbon group having 1 to 20 carbon atoms. R^(g)represents a hydrogen atom or a hydrocarbon group having 1 to 10 carbonatoms.

In the formula (d4), R^(d) is from the viewpoint of bettering solubilityin base oil, preferably a linear or branched alkylene group having 1 to8 carbon atoms, more preferably a linear or branched alkylene grouphaving 2 to 4 carbon atoms, even more preferably an alkylene grouphaving 2 carbon atoms or a branched alkylene group having 3 to 4 carbonatoms. Specifically, —CH₂CH₂—, —CH₂CH(CH₃)—, —CH₂CH(CH₂CH₃)—,—CH₂CH(CH₃)CH₂—, and —CH₂CH(CH₂CH₂CH₃)— are preferred; —CH₂CH₂—,—CH₂CH(CH₃)—, and —CH₂CH(CH₃)CH₂— are more preferred; and —CH₂CH₂—, and—CH₂CH(CH₃)— are even more preferred.

R^(e) and R^(f) each are, from the viewpoint of bettering extremepressure performance and bettering solubility in base oil, preferably alinear or branched alkyl group having 1 to 8 carbon atoms, morepreferably a linear or branched alkyl group having 3 to 6 carbon atoms.Specifically, they are preferably selected from groups of propyl,isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, hexyl,2-ethylbutyl, 1-methylpentyl, 1,3-dimethylbutyl and 2-ethylhexyl, andamong these, isopropyl, isobutyl and t-butyl are more preferred.

R^(g) is, from the viewpoint of bettering extreme pressure performanceand solubility in base oil, preferably a hydrogen atom, or a linear orbranched alkyl group having 1 to 4 carbon atoms. Specifically, ahydrogen atom and groups of methyl, ethyl, propyl, isopropyl, butyl,isobutyl and t-butyl group are preferred, and among these, a hydrogenatom, a methyl group and an ethyl group are more preferred.

<Other Additives for Lubricating Oil>

The lubricating oil composition of one embodiment of the presentinvention may contain any other additive for lubricating oil than theabove-mentioned components (B) to (D) within a range not detracting fromthe advantageous effects of the present invention.

Examples of such additives for lubricating oil include a rust inhibitor,a detergent dispersant, a viscosity index improver, an anti-foamingagent, a friction modifier, and a metal deactivator.

One alone or two or more kinds of these additives for lubricating oilmay be used either singly or as combined.

In the case where such additives for lubricating oil are added, thecontent of each additive for lubricating oil may be appropriatelycontrolled depending on the kind of the additive within a range notdetracting from the advantageous effects of the present invention, butis, based on the total amount (100% by mass) of the lubricating oilcomposition, generally 0.001 to 10% by mass, preferably 0.005 to 5% bymass, more preferably 0.01 to 2% by mass.

A lubricating oil composition prepared by blending an alkenylsuccinatein a base oil of PAG or POE suffers from worsening of waterseparability.

However, the lubricating oil composition of the present inventioncontains a base oil (A) that is well compatible with an alkenylsuccinateand therefore can effectively exhibit rust-preventing performance thatthe alkenylsuccinate has. In addition, even though an alkenylsuccinateis blended therein, the lubricating oil composition can still have goodwater separability.

In the lubricating oil composition of one embodiment of the presentinvention, the content of the alkenylsuccinate is, based on the totalamount (100% by mass) of the lubricating oil composition, preferably0.001 to 5.0% by mass, more preferably 0.005 to 2.0% by mass, even morepreferably 0.01 to 1.0% by mass, further more preferably 0.02 to 0.50%by mass.

Preferably, the lubricating oil composition of one embodiment of thepresent invention does not substantially contain a metal atom-containingcompound from the viewpoint of preventing sludge precipitation to occurin use for a long period of time in high-temperature environments.

Here, the metal atom in the “metal atom-containing compound” includes analkali metal atom, an alkaline earth metal atom and a transition metalatom.

In this description, “does not substantially contain a metalatom-containing compound” is a definition to deny an embodiment ofincorporating a metal atom-containing compound with a predeterminedobject but is not a definition to deny even a case of containing a metalatom-containing compound as an impurity.

However, the content of a metal atom-containing compound contained as animpurity is preferably as small as possible.

In the lubricating oil composition of one embodiment of the presentinvention, the content of a metal atom is, from the viewpoint ofpreventing sludge precipitation to occur in use for a long period oftime in high-temperature environments, based on the total amount (100%by mass) of the lubricating oil composition, preferably less than 100ppm by mass, more preferably less than 50 ppm by mass, even morepreferably less than 10 ppm by mass, further more preferably less than 5ppm by mass.

In this description, the content of a metal atom means a value measuredaccording to JPI-5S-38-92.

[Physical Properties of Lubricating Oil Composition]

The kinematic viscosity at 40° C. of the lubricating oil composition ofone embodiment of the present invention is preferably 5 to 300 mm²/s,more preferably 10 to 200 mm²/s, even more preferably 15 to 100 mm²/s.

The viscosity index of the lubricating oil composition of one embodimentof the present invention is preferably 90 or more, more preferably 100or more, even more preferably 105 or more, further more preferably 110or more.

When the lubricating oil composition of one embodiment of the presentinvention is tested according to the oxidation stability test (Dry-TOSTmethod) of ASTM D7873, the amount of sludge precipitated in 960 hoursafter the start of the test in an environment of 120° C. is preferably1.0 mg/100 ml or less, more preferably 0.7 mg/100 ml or less, even morepreferably 0.5 mg/100 ml or less.

The amount of the precipitated sludge is a value measured in accordancewith ASTM D7873 using a membrane filter having an average pore diameterof 1.0 μm.

When the lubricating oil composition of one embodiment of the presentinvention is tested under environment of 120° C. according to theoxidation stability test (Dry-TOST method) of ASTM D7873, the RPVOTresidual ratio in 960 hours after the start of the test is preferably65% or more, more preferably 70% or more, even more preferably 72% ormore.

RPVOT residual ratio is a value calculated according to the followingexpression.

[RPVOT residual ratio] (%)=[RPVOT time of sample after test]/[RPVOT timeof sample before test]×100

When the lubricating oil composition of one embodiment of the presentinvention is tested in a water separability test at a temperature of 54°C. according to JIS K2520, the demulsibility degree that indicates atime to be taken for an emulsion layer to reach 3 mL is preferably 15minutes or less, more preferably 10 minutes or less, even morepreferably 5 minutes or less.

The traction coefficient of the lubricating oil composition of oneembodiment of the present invention, as measured under the measurementconditions shown in the section of Examples given hereinunder, ispreferably 0.020 or less, more preferably 0.018 or less.

[Use of Lubricating Oil Composition, and Lubrication Method]

The lubricating oil composition of the present invention is used inturbomachinery, compressors (excepting refrigerators), hydraulicequipments, or machine tools.

Specifically, the lubricating oil composition of one embodiment of thepresent invention is favorably used as a lubricating oil (pump oil,turbine oil) for turbomachinery for use for lubrication ofturbomachinery such as pumps, vacuum pumps, blowers, turbocompressors,steam turbines, atomic force turbines, gas turbines, and turbines forhydraulic power generation; a bearing oil, a gear oil or a controlsystem operating oil for lubrication for compressors such as rotarycompressor and reciprocating compressors; a hydraulic actuation oil foruse for hydraulic machines; and a lubricating oil for machine tools foruse for hydraulic units of machine tools.

Namely, the present application also provides a use method of thefollowing [1],

[1] A method of using a lubricating oil composition, using a lubricatingoil composition containing a mineral oil (A) and a synthetic oil (B)that contains a polyalkylene glycol (B1) and a polyol ester (B2), inwhich the content of the mineral oil (A) is 5 to 95% by mass, inturbomachinery, compressors, hydraulic equipments, or machine tools.

Specific constitutions of the lubricating oil composition of the presentinvention, as well as specific exemplifications of turbomachinery,compressors, hydraulic equipments, and machine tools are as describedabove.

EXAMPLES

The present invention is described more specifically with reference toExamples, but the present invention is not limited to these Examples.

[Measurement Methods of Various Physical Property Values]

(1) Kinematic Viscosity, Viscosity Index

Measured and calculated in accordance with JIS K2283:2000.

(2) Number Average Molecular Weight (Mn)

Mn was measured in terms of standard polystyrene according to gelpermeation chromatography (GPC) under the following measurementconditions.

(Measurement Conditions)

Gel permeation chromatography apparatus: “1260 type HPLC” manufacturedby Agilent Co.

Standard sample: polystyrene

Column: One in which two of “Shodex LF404” were successively connectedto each other

Column temperature: 35° C.

Developing solvent: Chloroform

Flow rate: 0.3 mL/min

(3) Contents of Phosphorus and Metal Atoms

Measured in accordance with JPI-5S-38-92.

(4) Contents of Nitrogen Atom

Measured in accordance with JIS K2609.

Examples 1 to 7 and Comparative Examples 1 to 5

The mineral oil, synthetic oil, amine-based antioxidant, phosphoruscompound and other additives shown below were blended at the blendingratio shown in Table 1 and, and fully mixed to prepare lubricating oilcompositions (I) to (VII) and (i) to (v), respectively.

The details of the respective components used in the preparation of thelubricating oil compositions are as mentioned below.

(Mineral Oil)

“150N Mineral Oil”: mineral oil grouped in Group 2 of the API base oilcategory. Kinematic viscosity at 40° C.=30.6 mm²/s, viscosity index=104.

(Synthetic Oil)

“PAG”: Polypropylene glycol of which one end is sealed with butyl etherwhich is represented by H—(OCH(CHOCH₂)_(a)—OC₄H₉ (in the general formula(b-1), R^(B1) is a hydrogen atom, R^(B2) is a propylene group, R^(B3) isa n-butyl group, and b is 1). Kinematic viscosity at 40° C.=37.2 mm²/s,viscosity index=173, Mn=800.

“POE”: Trimethylolpropane triester (complete ester of trimethylolpropaneand carboxylic acid having 8 to 10 carbon atoms). Kinematic viscosity at40° C.=19.6 mm²/s, viscosity index=138.

(Amine-Based Antioxidant)

“Naphthylamine”: P-octylphenyl-α-naphthylamine. Nitrogen atomcontent=4.2% by mass.

“Diphenylamine”: Bis(p-octylphenyl)amine, a compound represented by thegeneral formula (c-2) where R^(x) and R^(y) are octyl group. Nitrogenatom content=3.6% by mass.

(Phosphorus Compound)

“Neutral phosphate ester”: Tris(p-isopropylphenyl)phosphate, in thegeneral formula (d1-2), p1 to p3 are 1, and R^(D11) to R^(D13) areisopropyl groups, wherein the isopropyl group is bonded to thepara-position. Phosphorus atom content=6.8% by mass.

“Acid phosphate amine”: Amine salt of a mixture of a compoundrepresented by the general formula (d2-1) and a compound represented bythe general formula (d2-2), and a compound represented by the generalformula (d3). (In the general formula (d2-1) and the general formula(d2-2), R^(a) and R^(b) each are an alkyl group having 8 or 10 carbonatoms, in the general formula (d3), R^(c) is an alkyl group having 12carbon atoms, q is 1 or 2.) Phosphorus atom content=4.8% by mass.

Thiophosphate 1: 3-Diisobutoxyphosphinothioylsulfanyl-2-methylprop anoicacid. Phosphorus atom content=9.3% by mass.

Thiophosphate 2:Ethyl-3-[{bis(1-methylethoxy)phosphinothioyl}thio]propionate. Phosphorusatom content=9.9% by mass.

(Other Additives)

“Rust inhibitor”: Alkenylsuccinate half ester.

“Anti-foaming agent”: Silicone-based anti-foaming agent, acryl-basedanti-foaming agent.

With respect to each of the prepared lubricating oil compositions,various physical property values shown in Tables 1 and 2 were measuredaccording to the above methods, and various properties of thelubricating oil compositions were evaluated by conducting the followingtests. The results are shown in Tables 1 and 2.

(1) Oxidation Stability Test (Dry-TOST)

The amount of sludge precipitated and the RPVOT residual ratio in 960hours after initiation of the test under environment of 120° C. wasmeasured in accordance with the oxidation stability test (Dry-TOST) ofASTM D7873.

The amount of the precipitated sludge was measured in accordance withASTM D7873 using a membrane filter having an average pore diameter of1.0 (provided by Millipore Corporation).

The RPVOT residual ratio was calculated according to the followingexpression.

[RPVOT residual ratio] (%)=[RPVOT time of sample after test]/[RPVOT timeof sample before test]×100

(2) Water Separability Test

A water separability test was conducted at a temperature of 54° C. inaccordance with JIS K2520 to measure the time (demulsibility unit: min)taken for an emulsion layer to reach 3 mL.

(3) Measurement of Traction Coefficient

Using an EHD oil film measuring device (available from PCS InstrumentsLtd.), a traction coefficient was measured under the followingmeasurement conditions.

Disc: diameter 46 mm, SAE AISI52100 steel

Ball: diameter 19 mm, SAE AISI52100 steel

Load: 20 N

Rolling speed: 2.0 m/s

Oil temperature: 60° C.

Slip ratio: 10%

(4) Wear Resistance Test

Using an FZG gear tester and according to ISO 14635-1, a load wasstepwise increased as prescribed, and a stage under a load to havegenerated scouring was evaluated. A higher stage of load indicates moreexcellent scouring resistance.

TABLE 1 Ex- Ex- Ex- Ex- Ex- Ex- Ex- ample ample ample ample ample ampleample 1 2 3 4 5 6 7 Lubricating Oil Composition (I) (II) (III) (IV) (V)(VI) (VII) Formu- Mineral Oil 150N mineral oil mass % 24.65 50.25 74.8589.00 48.00 48.00 48.00 lation Synthetic Oil PAG mass % 22.00 14.00 7.003.00 34.98 34.98 34.91 POE mass % 51.00 34.00 17.00 7.00 15.00 15.0015.00 Amine-based naphthylamine mass % 0.60 0.40 0.20 0.15 0.64 0.640.64 Antioxidant diphenylamine mass % 1.20 0.80 0.40 0.30 1.20 1.20 1.20Phosphorus neutral phosphate mass % 0.40 0.40 0.40 0.40 — — — Compoundacid phosphate mass% — — — — 0.03 — — amine salt thiophosphate 1 mass %— — — — — 0.03 — thiophosphate 2 mass % — — — — — — 0.10 Other rustinhibitor mass % 0.05 0.05 0.05 0.05 0.05 0.05 0.05 Additivesanti-foaming agent mass % 0.10 0.10 0.10 0.10 0.10 0.10 0.10 — totalmass % 100.00 100.00 100.00 100.00 100.00 100.00 100.00 Content of PAGin total amount mass % 30.1 29.2 29.2 30.0 70.0 70.0 69.9 (100% by mass)of synthetic oil Content of POE in total amount mass % 69.9 70.8 70.870.0 30.0 30.0 30.1 (100% by mass) of synthetic oil Mineral oil/(PAG +POE) (ratio by mass) — 0.34 1.05 3.12 8.90 0.96 0.96 0.96 Nitrogenatom-equivalent content mass 744 496 248 186 761 761 761 of amine-basedantioxidant ppm Phosphorus atom-equivalent mass 272 272 272 272 24 28 84content of phosphorus compound ppm Content of metal atom mass less lessless less less less less ppm than 5 than 5 than 5 than 5 than 5 than 5than 5 Properties of 40° C. kinematic mm²/s 23.6 25.2 27.4 29.6 25.325.2 25.3 Lubricating viscosity Oil Composition 100° C. kinematic mm²/s4.88 5.01 5.27 5.23 5.00 5.02 5.01 viscosity viscosity index — 134 128127 108 128 128 128 Eval- (1) Oxidation Sludge formation mg/100 0.2 0.40.5 0.5 0.2 0.5 0.2 uation stability test ml RPVOT residual % 85 88 7872 81 78 78 ratio (2) Water separability test, min 10 10 10 5 10 10 10demulsibility degree (3) Measurement of traction — 0.014 0.014 0.0170.018 0.013 0.014 0.014 coefficient, traction coefficient (4) Wearresistance text, — 6 6 6 6 12 12 12 FZG load stage

TABLE 2 Com- Com- Com- Com- Com- parative parative parative parativeparative Example Example Example Example Example 1 2 3 4 5 LubricatingOil Composition (i) (ii) (iii) (iv) (v) Formulation Mineral Oil 150Nmineral oil mass % 99.10 — — 99.47 99.47 Synthetic Oil PAG mass % —29.75 30.12 — — POE mass % — 68.00 68.00 — — Amine-based naphthylaminemass % 0.10 0.60 0.60 0.10 0.10 Antioxidant diphenylamine mass % 0.251.20 1.20 0.25 0.25 Phosphorus neutral phosphate mass % 0.10 0.40 — — —Compound acid phosphate amine salt mass % — — 0.03 0.03 — thiophosphate1 mass % — — — — 0.03 Other rust inhibitor mass % 0.05 0.05 0.05 0.050.05 Additives anti-foaming agent mass % 0.10 — — 0.10 0.10 — total mass% 100.00 100.00 100.00 100.00 100.00 Content of PAG in total amount mass% — 30.4 30.7 — — (100% by mass) of synthetic oil Content of POE intotal amount mass % — 69.6 69.3 — — (100% by mass) of synthetic oilMineral oil/(PAG + POE) (ratio by mass) — — 0 0 — — Nitrogenatom-equivalent content mass 145 744 744 145 145 of amine-basedantioxidant ppm Phosphorus atom-equivalent mass 272 272 14 14 28 contentof phosphorus compound ppm Content of metal atom mass less less lessless less ppm than 5 than 5 than 5 than 5 than 5 Properties ofLubricating 40° C. kinematic viscosity mm²/s 31.6 23.7 23.6 32.0 23.7Oil Composition 100° C. kinematic viscosity mm²/s 5.34 4.96 4.98 4.414.96 viscosity index — 101 139 139 102 139 Evaluation (1) OxidationSludge formation mg/100 1.2 0.3 0.3 27 19 stability test ml RPVOTresidual ratio % 60 95 95 29 95 (2) Water separability test, min 5 20 2020 20 demulsibility degree (3) Measurement of traction — 0.025 0.0120.012 0.024 0.025 coefficient, traction coefficient (4) Wear resistancetext, — 5 5 12 12 11 FZG load stage

The lubricating oil compositions prepared in Examples 1 to 7 wereexcellent in oxidation stability and had a strong effect of preventingsludge precipitation, and had excellent water separability. In addition,these have a low traction coefficient and showed an effect of improvingwear resistance.

On the other hand, the lubricating oil composition prepared inComparative Example 1 was poor in oxidation stability, and as comparedwith those in Examples, this caused much sludge precipitation and had alow RPVOT residual ratio. In addition, this is insufficient in point ofwear resistance.

The lubricating oil compositions prepared in Comparative Examples 2, 3,4 and 5 had good oxidation stability and wear resistance, but were poorin water separability, and among these, the composition of ComparativeExample 4 was especially poor in oxidation stability, and causedrelatively much sludge precipitation.

1. A lubricating oil composition comprising a mineral oil (A) and asynthetic oil (B) that comprises a polyalkylene glycol (B1) and a polyolester (B2); in which the content of the mineral oil (A) is from 5 to 95%by mass based on the total amount of the lubricating oil composition,and which is used in turbomachinery, compressors, hydraulic equipments,or machine tools.
 2. The lubricating oil composition according to claim1, wherein the content ratio of the component (B1) to the component (B2)[(B1)/(B2)] is, by mass, from 10/90 to 80/20.
 3. The lubricating oilcomposition according to claim 1, wherein the content ratio of thecomponent (A) to the total content of the component (B1) and thecomponent (B2) [(A)/((B1)±(B2))] is, by mass, from 0.05 to 19.0.
 4. Thelubricating oil composition according to claim 3, further comprising anantioxidant (C) that comprises an amine-type antioxidant (C1).
 5. Thelubricating oil composition according to claim 4, wherein the nitrogenatom-equivalent content of the component (C1) is, based on the totalamount of the lubricating oil composition, from 50 to 3,000 ppm by mass.6. The lubricating oil composition according to claim 1, furthercomprising one or more phosphorus compounds (D) selected from a neutralphosphate (D1), an acid phosphate (D2), an acid phosphate amine salt(D3) and a sulfur-phosphorus compound (D4).
 7. The lubricating oilcomposition according to claim 6, wherein the phosphorus atom-equivalentcontent of the component (D) is, based on the total amount of thelubricating oil composition, from 10 to 1,600 ppm by mass.
 8. Thelubricating oil composition according to claim 1, wherein the metal atomcontent is, based on the total amount of the lubricating oilcomposition, less than 100 ppm by mass.
 9. The lubricating oilcomposition according to claim 1, wherein, when the lubricating oilcomposition is tested in a water separability test at a temperature of54° C. according to JIS K2520, the demulsibility degree that indicates atime to be taken for an emulsion layer to reach 3 mL is 15 minutes orless.
 10. A method of using a lubricating oil composition, using thelubricating oil composition of claim 1 in turbomachinery, compressors,hydraulic equipments, or machine tools.